Cooler weather calls for this wonderfully rich, comforting and flavorful soup. It keeps well in the fridge for as long as a week and freezes well in individual containers, ready to defrost for a quick meal anytime.
Preheat the oven to 400 degrees. Line a baking sheet with aluminum foil.
In a large bowl, combine the sweet potatoes, parsnips, and carrots. Add the olive oil and toss to coat. Add the rosemary, thyme, salt, and pepper, tossing well.
Spread out the vegetables on the baking sheet and roast until tender and brown at the edges, 30 to 35 minutes. Rmove the baking sheet from the oven and allow to cool until just warm.
Working in batches, transfer some of the vegetables nad broth to a blender or food processor and blend until smooth. Pour each blended batch into a large saucepan.
When all of the vegetables have been pureed, heat the soup over low heat just until heated through.
To serve, ladle into bowls and top with Parmesan cheese if desired.